Error: the file or assembly Microsoft.Practices.EnterpriseLibrary.Validation or one of its dependencies not found

Scenario:

You are using Exclaimer Signature Manager Exchange Edition and find that messages are delivered without a signature appended. In the Exclaimer event log, the following message is observed when processing messages:

Solution:

1. Install the Enterprise Library from Microsoft (click here to download).
2. Using GacUtil, install the Microsoft.Practices.EnterpriseLibrary.Validation.dll into the GAC (GACUtil can be found in the Microsoft Windows SDK. Further details, and download links are available from Microsoft, here).
3. Browse to %ProgramData%\Exclaimer Ltd\Mail Disclaimers\Config2.
4. Take a backup copy of the CategorizerSettings.config file.
5. Using Notepad, open the original CategorizerSettings.config file.
6. Delete the following entry from the configuration file:
   
   

   <add type="Exclaimer.DirectoryServices.NoOpBackingStore, Exclaimer.DirectoryServices" name="NoOpBackingStore" />

7. Save and close the file.
8. Open the Windows Services Management console (run services.msc) and locate the Exclaimer Signature Manager Exchange Edition Configuration service.
9. Restart the Exclaimer Signature Manager Exchange Edition Configuration service.